. The biology of marine animals. Marine animals; Physiology, Comparative. 264 THE BIOLOGY OF MARINE ANIMALS gastropods (Crepidula, Pterocera). This is a hyaline rod extending into the stomach where it undergoes dissolution, thereby releasing its enzymes (22, 35, 48). The midgut gland of cephalopods (Loligo, AUoteuthis) produces digestive enzymes. The gland consists of two recognizably distinct parts known as liver and pancreas, both of which discharge into the caecum by a hepato- pancreactic duct. In structure they present the appearance of ramifying tubules; histologically, the secreting cell
. The biology of marine animals. Marine animals; Physiology, Comparative. 264 THE BIOLOGY OF MARINE ANIMALS gastropods (Crepidula, Pterocera). This is a hyaline rod extending into the stomach where it undergoes dissolution, thereby releasing its enzymes (22, 35, 48). The midgut gland of cephalopods (Loligo, AUoteuthis) produces digestive enzymes. The gland consists of two recognizably distinct parts known as liver and pancreas, both of which discharge into the caecum by a hepato- pancreactic duct. In structure they present the appearance of ramifying tubules; histologically, the secreting cells are distinctly different in the two tdc em \A * *»»ââ ** teb *W^a. jSrtH*&&, ss â ' *i'i 'v.,;" ac. f a/T7 vea ea Fig. Section through a Tubule of the Digestive Gland of Philine quadripartita, an Omnivorous Tectibranch Enzymes are secreted by the digestive gland, and digestion is completed intracellu- lar^, am, amoebocyte; ct, connective tissue; dc, digestive cell; ea, eb, excretory cells; em, excretory masses from excretory cells;/, fat droplet; ss, secretory spherules; tdc, teb, tips of digestive cells cut off from the epithelium; vea, vacuole with excretory material. (From Fretter (24).) regions. Proteolytic, amylolytic and lipolytic enzymes are produced by the gland. Preliminary digestion of foodstuffs takes place in the stomach, into which hepatopancreatic secretions are passed from the caecum, and digestion is completed in the latter. The digested food is absorbed in the caecum and intestine. In Octopus enzyme secretion and absorption both take place in the liver (16, 16a). Digestive diverticula are present in some of the lower chordates. Secre- tion is confined to the stomach in some tunicates, Ciona, but in Boltenia and Tethyum the gut diverticula are the primary organs of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of
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